Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature clamps as indicated by red arrows
Boiler CH thermostat set to MAX
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the differential as the boiler temperature reaches approximately 55°C
Expected differential approximately 22°C or less.
Note:
To reduce the time taken for this test some radiators could be turned off temporarily.